I had an interesting conversation with a prospective young writer and she was asking about how I develop my characters. I told her that I like to think of them as well crafted pieces of the whole novel. That there must be a chemistry between the characters in each chapter. It didn't matter if the characters are on the side of good or bad (and frankly there are few who are so clearly defined - as most are a bit of both) but the chemistry must be there. If when you finish the chapter and the interaction between the characters leaves you with a hum-ha feeling... throw it away and start again. The right chemistry between the characters is everything. When the right chemistry is there the interaction of the characters will be electric and captivate the reader. I personally think that it must be electric from the start to the finish not just in one chapter... their situations may generate the lightening or it may be their relationships but lightening is essential... even if it's shocking.